The present invention relates to methods and apparatuses for delivering a dose of aerosolized medication by inhalation into the lungs of a patient, and more particularly to an internal vortex mechanism for an inhaler device.
Aerosols are increasingly being used for delivering medication into the lungs for therapeutic treatment of the body. For example, in the treatment of asthma, inhalers are commonly used for delivering bronchodilators such as xcex22 agonists and anti-inflammatory agents such as corticosteroids. Two types of inhalers are in common usexe2x80x94metered dose inhalers (MDIs) and dry powder inhalers (DPIs).
In a conventional MDI device, the medication is provided by the pharmaceutical manufacturer in a pressurized aerosol canister, with the medication being suspended or dissolved in a liquid propellant such as a chloro fluorocarbon (CFC) or hydrofluoroalkane (HFA). The canister includes a metering valve having a hollow discharge stem which can be depressed inward into the canister to discharge a metered volume of propellant-medication mixture in the form of an aerosol comprising fine droplets of propellant in which particles of the medication are suspended or dissolved.
A conventional MDI for use with such a canister includes a housing having an actuator and nozzle. The canister is inserted into the housing with the hollow discharge stem of the canister being received in a bore in the actuator. Depressing the closed end of the canister causes the stem to be pushed inward into the canister so that a metered volume of medication is discharged through the nozzle. The housing further defines a flowpath in fluid communication with the nozzle, the flowpath having an outlet at a mouthpiece portion of the housing, such that the aerosolized medication may be inhaled after it exits the mouthpiece portion. The patient either inserts the mouthpiece into the mouth with the lips closed around the mouthpiece, or holds the mouthpiece at a slight distance away from an open mouth. The patient then depresses the canister to discharge the medication, and simultaneously inhales.
While generally good for many applications, existing MDIs suffer from a number of significant disadvantages. One problem with existing MDIs is poor delivery efficiency of the medication. It has been estimated that on average, with existing MDIs, only about 10 percent of the medication dose which is dispensed from the canister actually reaches the lungs where it can achieve the intended result. A significant portion of the medication impacts and sticks to the inner surfaces of the MDI device. This makes MDIs less than optimal for delivering expensive medication.
To reduce the amount of medication sticking to the inner surfaces of the MDI device, Applicants"" co-pending application Ser. Nos. 08/954,352, 09/326,538, 09/326,531, disclose a series of internal vanes mounted on the inner surface of the MDI device, near the point of exit of the medication into the MDI device. Outside air is directed over the vanes during medication dispensing to create a circumferential-swirling turbulent boundary layer along the inner surface of the MDI device to minimize the impaction of medication onto the inner surfaces. Although the vanes minimize the impaction of medication, they also add to the cost and complexity of the MDI device.
Accordingly, it is an object of the present invention to provide a method and apparatus for delivering an aerosolized medication in which the respirable fraction of the metered dose (i.e., the fraction in the form of particles of the optimum size) is maximized at the exit of the apparatus.
Another object of the invention is to provide a method and apparatus for delivering an aerosolized medication in which impaction and sticking of medication on the inner walls of the apparatus is minimized.
Yet another object of the present invention is to provide an MDI device with a circumferential-swirling turbulent boundary layer of air along the inner surface of the MDI device in a cost effective and simple manner.
The above and other objects of the invention are achieved by the method and apparatuses of the invention that follow, in which flow control techniques and devices are used primarily to limit impaction and sticking of medication to the inner surfaces of an MDI device, and also aid in:
mixing ambient air with the medication and help disperse the plume of aerosolized medication;
evaporating the aerosol propellent of the medication;
directing the air/medication mixture to the mouthpiece for inhalation by a patient.
In one embodiment of the invention, an aerosol flow control apparatus includes a housing having an open end and a generally tubular conduit with a wall including an inner surface, a medication dispenser disposed within the housing and adapted to dispense a dose of aerosolized medication into the conduit, and a plurality of vortex generators formed within the wall downstream from the medication dispenser. The vortex generators establish a circumferential-swirling turbulent air flow along the inner surface upon an air flow being established through the open end.
In another embodiment of the present invention, an aerosol flow control apparatus includes a housing having a conduit defined by a wall including an inner and an outer surface, an open end adapted to be inserted into the mouth of a user and a substantially closed end remote from the open end. The apparatus also includes a medication dispenser supported in the housing and adapted to dispense a dose of aerosolized medication into the conduit, a plurality of air inlets positioned on the outer surface of the conduit, and a plurality of vortex generators positioned within the wall of the conduit downstream of the medication dispenser. The vortex generators are in fluid communication with the air inlets. An inspiratory effort exerted on the open end of the conduit causes air to flow over the vortex generators to establish a circumferential-swirling turbulent boundary layer flow along the inner surface of the conduit to reduce impaction and sticking of medication thereon.
In yet another embodiment of the present invention, a method for delivering a dose of medication in an aerosol flow control apparatus having a housing with a conduit including an inner and an outer surface, an open end adapted to be inserted into the mouth of a user, a substantially closed end remote from the open end, and a medication dispenser supported in the housing and adapted to dispense a dose of aerosolized medication into the conduit. The method includes the steps of discharging a dose of medication from the medication dispenser to form a plume of aerosolized medication within the conduit, and at least during the discharging step, providing an air flow along the inner surface of the conduit by an inspiratory effort exerted on the open end of the conduit. The air flow being drawn through a plurality of air inlets formed on the outer surface of the conduit adjacent the juncture between the conduit and the closed end of the housing and over a plurality of vortex generators formed within the wall downstream of the medication dispenser and having outlets adjacent the inner surface of the conduit. A circumferential-swirling turbulent boundary layer flow is created along the inner surface of the conduit to reduce impaction and adhesion of medication thereon.
Still another embodiment of the present invention includes an aerosol flow control apparatus having a housing including an open end and a generally tubular conduit, where the conduit includes a wall having an inner surface, and a plurality of air inlets in fluid communication with ambient air outside the conduit. The apparatus also includes a medication dispenser assembly disposed within the housing and adapted to dispense a dose of aerosolized medication into the conduit, and a plurality of vortex generators positioned within the wall of the conduit downstream of the medication dispenser. Each vortex generator includes a first generally pyramid-like portion having an apex and an open base forming an outlet located on the inner surface and a second generally pyramid-like portion having an apex and an open base in fluid communication with a corresponding air inlet. The apexes of the pyramid shaped portions overlap to form an opening allowing fluid communication between the pyramid-like portions, where the vortex generators and the air inlets cooperate to establish a circumferential-swirling turbulent air flow along the inner surface upon an air flow being established through the open end.
One of the unique features of the present invention is the decreased cost of MDI devices using the vortex generators according to the present invention, as well as the simplification of their manufacture. Specifically, the unique pyramid shapes of the vortex generators are inexpensive to produce and allow for easy fabrication/modification in plastic molding. By molding the vortex generators within the wall of the conduit, the cost of the extra material when molding vanes non the inner wall of the conduit is eliminated. In addition, the complexity of the mold for producing the conduit is decreased allowing easier manufacture of the mold and easier production of the MDI device.
The present invention results in easy manufacture using plastic injection molding, where the unique vortex generator design allows for easy pull for fabrication in plastic.
These and other objects and advantages of the present invention shall become more apparent from the accompanying drawings and the description thereof.